St James's Palace confirms that the Duchess of Cambridge is pregnant but has been hospitalised suffering from a severe form of morning sickness

The Duchess of Cambridge, Kate Middleton, is expecting her first baby.

In a statement from St James's Palace, the royal family confirmed: "The Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting a baby. The Queen and Duke of Edinburgh, the Prince of Wales and members of both families are delighted with the news."

The Palace also revealed that Kate Middleton is currently suffering from a severe form of morning sickness called hyperemesis gravidarum.

"The Duchess was admitted this afternoon to King Edward VII Hospital in central London with hyperemesis gravidarum," said the statement. "As the pregnancy is in its very early stages, Her Royal Highness is expected to stay in hospital for several days and will require a period of rest thereafter."

Hyperemesis gravidarum is a rare and extreme form of morning sickness estimated to effect just a fraction of one per cent of pregnant women worldwide. Symptoms include "unrelenting, excessive pregnancy-related nausea and/or vomiting" and can result in dehydration, malnutrition and potentially serious complications.

Mothers suffering from the condition who do not gain sufficient weight during pregnancy tend to give birth earlier, to lighter babies.